feat(httpclient): initial stable release v0.9.0

Resilient HTTP client with circuit breaking, exponential-backoff retry, X-Request-ID propagation, and a generic typed JSON helper.

What's included:
- Client interface with Do(req) method; New(logger, cfg) and NewWithDefaults(logger) constructors
- Config struct with env-tag support for timeout, dial timeout, retry, and circuit breaker parameters
- Retry via avast/retry-go/v4 with BackOffDelay; triggers only on network errors and HTTP 5xx
- Circuit breaker via sony/gobreaker wrapping the full retry loop; open circuit → xerrors.ErrUnavailable
- X-Request-ID header propagated automatically from context via logz.GetRequestID on every attempt
- DoJSON[T](ctx, client, req) generic helper for typed JSON request/response with xerrors error mapping
- MapStatusToError(code, msg) exported function mapping HTTP status codes to xerrors types

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

README.md

@@ -0,0 +1,57 @@
+# httpclient
+
+Resilient HTTP client with automatic retry and circuit breaking.
+
+## Install
+
+```
+go get code.nochebuena.dev/go/httpclient
+```
+
+## Usage
+
+```go
+client := httpclient.NewWithDefaults(logger)
+// or with custom config:
+client = httpclient.New(logger, httpclient.Config{
+    Name:        "payment-api",
+    MaxRetries:  3,
+    CBThreshold: 10,
+})
+
+resp, err := client.Do(req)
+```
+
+## Typed JSON helper
+
+```go
+order, err := httpclient.DoJSON[Order](ctx, client, req)
+```
+
+## Error mapping
+
+```go
+httpclient.MapStatusToError(404, "not found") // → xerrors.ErrNotFound
+```
+
+| HTTP status | xerrors code |
+|---|---|
+| 404 | `ErrNotFound` |
+| 400 | `ErrInvalidInput` |
+| 401 | `ErrUnauthorized` |
+| 403 | `ErrPermissionDenied` |
+| 409 | `ErrAlreadyExists` |
+| 429 | `ErrUnavailable` |
+| 5xx | `ErrInternal` |
+
+## Configuration
+
+| Env var | Default | Description |
+|---|---|---|
+| `HTTP_CLIENT_NAME` | `http` | Circuit breaker name |
+| `HTTP_TIMEOUT` | `30s` | Overall request timeout |
+| `HTTP_DIAL_TIMEOUT` | `5s` | TCP dial timeout |
+| `HTTP_MAX_RETRIES` | `3` | Retry attempts |
+| `HTTP_RETRY_DELAY` | `1s` | Base retry delay |
+| `HTTP_CB_THRESHOLD` | `10` | Consecutive failures before open |
+| `HTTP_CB_TIMEOUT` | `1m` | Time before half-open retry |